HI all, im working on a 1974 280. starts fine but when is under pressure it back fires all over the place. dont know if this is timing or bad wires which are kinda bad or what? also i have a couple of vacuum lines not hooked up. they are in the front driver side coming from right behind headlamp. colors are a green one and then there are 2 clear ones. anyone happen to have a vacuum diagram or something? any help is appreciated. thanks

Oh btw... this is my first post, little backround on the car... my grandma was taking care of some lady and she gave it to my grandma. odo reads 14,000 so thats pretty cool. just trying to get it running good.

The backfire could be a timing issue; timing problems will occur if the distributor advance or retard vacuum lines are not working properly. Do you have the two and three way switches mounted on the right side fender well? They are wired to activate at low and high RPMs and route vacuum. Good luck finding a vacuum diagram. I have been searching for months for one. I have researched on line and at the library and still no luck there. I keep hoping someone could take a picture of theirs and post it.

ya im in the process of giving it a tune up, plugs cap rotor etc... plug wires are next...
@vacuum diagram, unfortunatly thats not specific enouph. im thinking abt just getting a chilton book...
ya it would be nice if i could find one in person! that way i could check it out. im in socal so if anyone has one around let me know

abt the timing i fiddled with it and nothing seems to be resolving it, even messed with fuel.